A superconducting motor is a motor that rotates a rotor using a superconducting magnet. A superconducting motor is used in a state where a superconducting magnet is cooled to or below a critical temperature of a superconducting material that constitutes the superconducting magnet. The superconducting magnet is cooled using a refrigerant with a boiling point that is equal to or lower than the critical temperature. After cooling the superconducting magnet, the refrigerant is cooled to or below the critical temperature by a cooling circuit and is once again used to cool the superconducting magnet.
When the critical temperature of a superconducting material is higher than a boiling point of liquid nitrogen, liquid nitrogen can be used as the refrigerant. The boiling point of liquid nitrogen, 77 K, has a relatively small difference from the boiling point of liquefied natural gas (111 K). In consideration thereof, if the refrigerant after cooling the superconducting magnet is to be cooled using a heat exchange between the refrigerant (liquid nitrogen) and liquefied natural gas, energy required for bringing a temperature of the refrigerant down to or below the critical temperature can be reduced. An example of such a technique is disclosed in Japanese Unexamined Patent Publication No. 2007-83851.
When a compressor used in a process of liquefying natural gas is driven by a superconducting motor, cost required by the process of liquefying natural gas can be lowered by reducing energy for bringing a refrigerant down to or below the critical temperature. Since a major portion of the cost of liquefied natural gas is incurred in the process of liquefying natural gas, by reducing the cost of this process, a significant reduction in the cost of liquefied natural gas can be achieved.
In a similar manner, in a power generation system provided with a turbine which rotates using energy generated by burning natural gas created by liquefying liquefied natural gas retrieved from a tank and a superconducting generator which is driven by a rotation of the turbine and which generates power, power generation cost can be lowered by reducing energy for bringing a refrigerant down to or below the critical temperature.